1. Field of the Invention
This invention relates to a shift control system for a change gear auxiliary transmission section and, in particular, relates to a shift control system for a splitter type change gear auxiliary transmission section permitting preselection of an auxiliary section shift or gear change which shift or gear change will be executed upon achievement of enabling conditions, such as a torque break permitting disengagement of the previously engaged auxiliary section gear and achieving synchronization or substantial synchronization of the clutch members associated with the preselected gear.
2. Description of the Prior Art
Compound transmissions of the splitter or range type, or a combination thereof, are well known in the prior art as may be see by reference to U.S. Pat. Nos. 3,105,395; 3,648,546; 3,799,002; 2,932,988 and 3,229,551, the disclosures of all of which are hereby incorporated by reference. The main section of such transmissions are typically controlled by the operator by means of a shift lever operating directly upon shift rails or by electric and/or pneumatic means, and the auxiliary section is typically shifted by means of a control lever or button located on or adjacent the shift lever knob for operating the remote auxiliary shift mechanism, either pneumatically, hydraulically and/or electrically. Examples of such shift control systems for compound transmissions are well known in the prior art and examples thereof may be appreciated in greater detail by reference to U.S. Pat. Nos. 2,637,222; 2,763,290; 3,648,546; 3,799,002; 3,921,469; 3,983,799 and 4,194,410, the disclosures of all of which are hereby incorporated be reference.
Blocked change gear transmissions of both the simple and the compound types are also well known in the prior art as may be seen by reference to the above-mentioned U.S. Pat. Nos. 3,799,002; 3,921,469; 3,983,799 and 4,194,410. Blocked transmissions of this type typically utilize jaw clutch assemblies which may be axially shifted against a resilient bias for positive clutch engagement upon sensing of a synchronous or substantially synchronous rotation therebetween. The structure and function of the resilient biased jaw clutch assemblies and of the blockers carried thereby are well known in the prior art and form no part of the present invention. The prior art for change gear transmissions, especially the auxiliary sections of change gear transmissions, are highly advantageous as they permit the operator to preselect a gear change which gear change will be executed upon subsequent achievement of certain operating conditions, such as a break in the torque allowing disengagement of the previously engaged gear and achievement of substantially synchronous rotation of the jaw clutch members associated with the preselected gear.
A pressurized fluid shift control system for preselect type shifting of an auxiliary transmission section is illustrated in U.S. Pat. No. 4,555,959, the disclosure of which is hereby incorporated by reference. This control system utilizes Pilot valves to provide rapid response and preselection prohibit valves which will block fluid communication between the pilot valves and the shifting mechanism until such time as a predetermined condition occurs such as the occurrence of a signal indicative of the operator stroking the vehicle master clutch.
While the auxiliary transmission section shift control systems of the prior art did provide acceptable performance, for certain situations, such as for controlling the preselectable shifting of splitter type auxiliary transmission sections, the prior art systems were of a more complicated and/or expensive structure than desired.